The present invention relates generally to optical communications. The present invention relates more particularly to a method and apparatus for measuring the wavelength and power of individual channels in dense wavelength division multiplexing (DWDM) optical communications systems and the like.
The use of dense wavelength division multiplexing (DWDM) in optical communications systems, such as those using fiber optics, is well-known. According to dense wavelength division multiplexing, a plurality of different wavelengths of light are transmitted via a single medium, such as an optical fiber, simultaneously, so as to substantially enhance communications bandwidth. In this manner, a much greater amount of information may be transmitted than is possible using a single wavelength multiplexing optical communications system.
It is beneficial to monitor the wavelength and power of each separate channel utilized in a wavelength division multiplexing communications system. Monitoring the wavelength and power assures that these parameters are within optimal operating ranges, so as to facilitate the maintenance of reliable communications at approximately maximum bandwidth.
As those skilled in the art will appreciate, when the wavelength of a communications channel drifts away from its nominal center frequency, then that channel will be less efficiently detected by a receiver at the nominal filter passband. Further, as the wavelength of a given channel drifts away from its nominal center frequency, that channel may tend to interfere with other channels, particularly those other channels at adjacent or nearby wavelengths, and cause crosstalk. Therefore, it is desirable to monitor the wavelength of each communications channel in a wavelength division multiplexing communications system, so as to facilitate maintaining the wavelength of the channel as close as possible to its nominal center frequency.
Similarly, as the power of a channel drifts away from its nominal value, the ability to detect the information content of the channel can be substantially degraded. For example, substantially reduced power may place the channel below the threshold at which it may be reliably detected. Conversely, power which is too high may result in saturation of a receiver""s detectors. As such, power must remain within the dynamic range of a receiver""s detector in order for a channel to be reliably detected. Therefore, it is desirable to monitor the power of each channel in a wavelength division multiplexing communications system, so as to facilitate maintaining the power of the channel as close as possible to its nominal value.
It is known to use devices such as optical spectral analyzers and multi-channel optical wavelength meters to monitor the wavelength of a channel in a wavelength division multiplexing communications system. However, as those skilled in the art will appreciate, both optical spectral analyzers and multi-channel optical wavelength meters suffer from inherent disadvantages which detract from their suitability and desirability for such use. For example, both optical spectral analyzers and multi-channel optical wavelength meters utilize mechanical scanning mechanisms. Those skilled in the art will appreciate that such mechanical scanning mechanisms tend to respond undesirably slowly to changes in wavelength. Moreover, such slow response makes contemporary optical spectral analyzers and multi-channel optical wavelength meters less suitable for real time monitoring and control of optical communications systems. Furthermore, both optical spectral analyzers and multi-channel optical wavelength meters are comparatively large in size (at least in part due to their use of mechanical scanning mechanisms) and are undesirably expensive to purchase, install and maintain.
It is also known to use phased array waveguide gratings (PAWGs) to effect the measurement of wavelengths in wavelength division multiplexing optical communications systems. Such phased array waveguide gratings utilize a crossover property thereof to monitor the wavelength of individual channels in a wavelength division multiplexing optical communications system. Phased array waveguide gratings do not utilize mechanical scanning mechanisms like those of optical spectral analyzers and multi-channel optical wavelength meters, and therefore tend to be less expensive to purchase, install and maintain, as compared to optical spectral analyzers and multi-channel optical wavelength meters. However, as those skilled in the art will appreciate, phased array waveguide gratings have two passband peaks associated with each channel spacing, thus making the crossover point difficult to control. Further, the wavelength range of a phased array waveguide grating is typically less than 50% of the signal channel spacing, which results in poor performance of the phased array waveguide grating.
In view of the foregoing, it is desirable to provide a method and apparatus for measuring the wavelength of each channel in a wavelength division multiplexed optical communications system, which is comparatively inexpensive to purchase, install and maintain and which provides satisfactory performance. It is further desirable to provide such a system which is additionally capable of measuring the power of each wavelength division multiplexed channel.
The present invention specifically addresses and alleviates the above-mentioned deficiencies associated with the prior art. More particularly, the present invention comprises a method and device for measuring a wavelength of an electromagnetic signal, wherein first and second waveguides are configured such that a portion of an electromagnetic signal which is transmitted through the first waveguide is separated from a remaining portion of the electromagnetic signal in the first waveguide and is communicated to the second waveguide. A portion of the electromagnetic signal (now in the second waveguide) which was separated from the remaining portion of the electromagnetic signal (still in the first waveguide) is subsequently at least partially recombined with the remaining portion of the electromagnetic signal (in the first waveguide), after the separated portion has traveled a distance which is different from the distance traveled by the remaining portions.
A first sensor is configured to measure the power of the electromagnetic signal in the first waveguide after at least a portion of the separated electromagnetic signal in the second waveguide has been recombined with the remaining electromagnetic signal in the first waveguide.
Similarly, a second sensor is configured to measure the power of the electromagnetic signal in the second waveguide after at least a portion of the separated electromagnetic signal in the second waveguide has been recombined with the remaining electromagnetic signal in the first waveguide.
According to the preferred embodiment of the present invention, the first and second waveguides are formed upon and integrated with a common, i.e., the same, semiconductor substrate.
These, as well as other advantages of the present invention will be more apparent from the following description and drawings. It is understood that changes in the specific structure shown and described may be made within the scope of the claims without departing from the spirit of the invention.